Circuit board material and method of making

Abstract

An improved multilayered circuit board material and process for making that material is disclosed. The material includes an insulating material support layer, an electrical resistance material layer adhering to the support layer, and a conductive material layer adhering to the resistance material layer and in intimate contact with that layer. The electrical resistance material layer comprises electroplated nickel-phosphorous containing up to about 30% by weight of phosphorous; however, no appreciable amounts of sulfur are present within at least the top about ten atomic layers of the electrical resistance material layer. As a result, the stability of the electrical resistance material layer is significantly increased. In addition, the electroplating bath does not contain chloride salts resulting in decreased pitting in the electrical resistance material layer.

We claim: 
     
       1. A method of electroplating a circuit board substrate with nickel-phosphorous, the method comprising the steps of: (a) cleaning the substrate; and   (b) electroplating the substrate in a bath consisting essentially of an aqueous solution of a nickel ion source, H 3  PO 3  and H 3  PO 4 , wherein the bath is substantially sulfate and chloride free.   
     
     
       2. The method according to claim 1 wherein the concentration of Ni ions to PO 3  ions in the bath ranges from 0.25/0.50 to 1.25/2.50. 
     
     
       3. The method of electroplating a substrate according to claim 1 including the further step of forming the nickel ions in the bath by dissolving nickel carbonate in the bath. 
     
     
       4. A method according to claim 1 wherein the bath consists essentially of a solution of nickel carbonate, H 3  PO 3  and H 3  PO 4 . 
     
     
       5. The electroplated substrate according to claim 1, wherein the resistance change after 1000 hours at 70° C. is 0.2%, wherein the temperature coefficient of resistance from -65° C. to 125° C. is -10 ppm/° C., and wherein the current noise is less than 0.02 microvolts/volt. 
     
     
       6. An electroplating bath used for electroplating a nickel-phosphorous resistance layer on a printed circuit board material stock substrate, the bath consisting essentially of a nickel ion source, phosphoric acid and phosphorous acid, and wherein the bath is substantially sulfate and chloride free. 
     
     
       7. The electroplating bath according to claim 6 wherein the nickel ions are formed by dissolving nickel carbonate in the bath, and wherein the bath is aqueous. 
     
     
       8. A substantially sulfate and chloride free electroplating bath used for electroplating a nickel-phosphorous resistance layer on a substrate, the bath consisting essentially of an aqueous solution of 1M nickel ion source, 2M phosphorous acid and 0.5M phosphoric acid. 
     
     
       9. A process for electroplating an electrical resistance material layer composition on a substrate, the process including the step of electroplating the substrate in a substantially sulfate and chloride free bath consisting essentially of 1 Molar nickel carbonate, 2 Molar phosphorous acid, and 0.5 Molar phosphoric acid, wherein the bath temperature ranges from 70° C. to 75° C., the time of electroplating is 30 seconds and the RsOhms/square ranges from 25 to 50. 
     
     
       10. The process according to claim 9 wherein the bath temperature is 70° C. and the RsOhms/square is 50. 
     
     
       11. The process according to claim 9 wherein the bath temperature is 75° C. and the RsOhms/square is 25. 
     
     
       12. The substrate and electroplated electrical resistance material layer formed thereon according to the process of claim 11. 
     
     
       13. The substrate and electrical resistance material layer formed thereon according to the process of claim 9. 
     
     
       14. A method for forming a printed circuit board material having a nickel-phosphorous electrical resistance material layer in contact with a conductive material and an insulating substrate, the method comprising: forming an electroplating bath consisting essentially of a nickel ion source, phosphoric acid and phosphorous acid, the bath being substantially chloride and sulfate free;   electroplating to form the electrical resistance material layer on the conductive material in the electroplating bath; and   adhering the resultant electroplated conductive material to an insulating substrate such that the electrical resistance material layer is in operative contact with the insulating substrate.   
     
     
       15. The printed circuit board material product formed according to the method of claim 14. 
     
     
       16. A method of electroplating a nickel-phosphorous composition on a circuit board substrate including the following steps: (a) cleaning the substrate;   (b) forming an electroplating bath consisting essentially of H 3  PO 4 , H 3  PO 3 , and a nickel ion source, and wherein the bath is essentially free of sulfate and chloride ions; and   (c) electroplating the composition onto the substrate in the bath.   
     
     
       17. A method according to claim 16 wherein the nickel ion source is nickel carbonate.